Caesium or cesium is a chemical element with symbol Cs and atomic number 55. It is a soft, silvery-gold alkali metal with a melting point of 28 °C, which makes it one of only five elemental metals that are liquid at or near room temperature.

Symbol: Cs
Electron configuration: [Xe] 6s1
Melting point: 83.19°F (28.44°C)
Atomic number: 55
Discovered: 1860
Boiling point: 1,240°F (670.8°C)
Atomic mass: 132.90545 ± 0.0000002 u

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